Why Black Holes Spin So Fast - Black Hole Messier 87 (M87) - Spinning Black Holes Explained

The Chandra X-ray Observatory has spotted a supermassive black hole that has shattered all the records of rotational speed. This black hole is spinning at 99% of the speed of light. The black hole, named Messier 87 or M87, is 7 billion times more massive than our sun. The black hole, M87, also named as Povehi, is 54 million light-years away from Earth. Guys, just imagine such a massive object spinning at this insanely high speed. Actually, all spinning black holes spin at extremely high speed, which is comparable to the speed of light. It is possible for a black hole to rotate thousands of times in just one second. Actually, it's not that easy to imagine this unimaginably high speed of rotation of black So, for comparison, let me remind you that Earth takes 24 hours to complete only one rotation on its axis. Now compare this to the spinning speed of black holes, which are millions or billions of times more massive than the sun, and making hundreds or even thousands of rotations per second. Almost all the celestial objects spin on their axis. For example, all the planets, satellites, stars, and even the galaxies spin. But what makes the spinning of black holes special is their incredibly high speed of rotation, that almost approaches the limit of maximum possible speed, the speed of light. But now the question arises, what causes these immensely massive black holes spin so fast? Actually, the answer lies in the conservation of angular momentum. The law of conservation of angular momentum says, the angular momentum of a body remains constant if the resultant external torque on the body is zero. The formula to calculate the angular momentum is I multiplied by omega. Here, I is the moment of inertia, and omega is the angular velocity. So, according to the conservation of angular momentum, I omega is equals to constant. Here, I is given by the product of mass of the object, and square of its perpendicular distance from the axis of rotation. So, we can write I is equals to m r square. You can see from the formula, that as the r decreases, the moment of inertia I also decreases. But, according to the conservation of angular momentum, product of I and omega must be constant. Here, I has decreased due to decrease in r. So, to keep the I omega constant, omega has to increase. The same rule is applied on the spinning of black holes, as all the heavenly bodies like planets, stars, galaxies or black holes are created when moving clouds of gases and dust come together under the gravitational pull. They finally form a spinning solid object, like a planet or a star. Please note that it is almost impossible to have the zero resultant torque on the planets or stars as they are formed from the randomly moving clouds of dust and gases. This initial unbalanced external force gives them a spin. And we know that the black holes are formed from the dying stars. So, these black holes get their spin from the spinning star. But, why black holes spin so fast after all? Actually, when the black hole starts to collapse under its own gravitational pull, its whole mass comes closer to the axis of rotation. Now, look at the formula of conservation of angular momentum. As the r decreases, the moment of inertia I also decreases. But, to keep I omega constant, the angular velocity omega increases. As the density of black hole approaches infinity, its whole mass reaches very close to the axis of rotation. And hence, its perpendicular distance from the axis of rotation decreases drastically. Because of this, the rotational speed of the black hole approaches the ultimate speed limit, the speed of light. So, friends, now you know why all the celestial bodies spin and why the black holes spin so fast. I hope you liked the video. If you really liked it, please like and share it. And subscribe my channel Engineering Made Easy, if you don't want to miss any of my video. Thank you for watching.